There have been proposed medical suture needles which have various shapes (e.g., a straight needle and a curved needle) and dimensions corresponding to an applied portion. The curved needle is formed so as to be curved at a predetermined angle and radius. There have been proposed a round needle of circular cross-section and a cornered needle of polygonal cross-section.
The medical suture needle has a body portion held by a needle holder, a sharp needle point for penetrating a biotissue, and a needle point portion which has a thickness decreased from the body portion to the needle point. The body portion typically has a cross section formed in flat shape so as to be stably held by the needle holder.
In a bending method of a medical suture needle as described in Patent Document 1, there is used a bending device which has a cylindrical winding roll which defines the curved shape of the medical suture needle, an auxiliary roll which is pressingly contacted with the winding roll, and a metal belt arranged between the winding roll and the auxiliary roll. A straight needle-shaped material is inserted between the winding roll and the metal belt, and then the winding roll rotates a predetermined angle clockwise. The inserted straight needle-shaped material can be bent. The winding roll is rotated counterclockwise to take out the curved medical suture needle.
A bending method described in Patent Document 2 is preferably used for bending a medical suture needle with a blade which has a triangular cross section. In the bending method, an elastic member adheres to one surface configuring the triangular shape. The suture needle is arranged so as to bring the surface into contact with a cylindrical bending top. The suture needle is inserted between the bending top and a belt.
In the technique described in Patent Documents 1 and 2, a portion of the outer circumferential surface or one surface of the straight needle-shaped material is brought into contact with the surface of the cylindrical winding roll or the bending top. In this state, the straight needle-shaped material is pressed by the belt from the opposite side and is then bent. The bending shape of the medical suture needle is defined by the outer diameter of the winding roll or the bending top.
The bending shape of the medical suture needle is defined by the outer diameter of the winding roll or the bending top. This does not mean that the outer diameter of the winding roll or the bending top and the diameter of the curved inner surface of the medical suture needle are the same. Due to springback caused in the material of the medical suture needle, the diameter of the curved inner surface of the medical suture needle is typically larger than the outer diameter of the winding roll or the bending top.
[Patent Document 1] Japanese Patent Application Publication (JP-B) No. 07-004388
[Patent Document 2] Japanese Patent No. 2849143